Increased nitrate reductase A activity as a sign of membrane alteration in early blocked asporogenous mutants of Bacillus subtilis.

Nitrate reductase (Nar) activity, and its regulation, have been studied in B. subtilis and Spo0 mutants derived from it. The mutants are blocked at the stage zero of sporulation. The only Nar detected was the membrane-bound Nar A, which has been solubilized and purified. The enzyme itself, and its regulation, seem to be the same in Spo+ and Spo0 strains. Under all conditions tested, however, the mutants were hyperproducers of Nar A. Whether produced by a Spo+ or a Spo0 strain, the purified enzyme has the same Km on nitrate, and the same heat inactivation kinetics. In situ in membrane vesicles of a Spo+ strain, it displays the same Km and its thermoinactivation is exponential. In mutant vesicles, however, two Km's are observed, one normal and one five times higher, and thermoinactivation follows an initial period of activation. The higher Km disappears after heat activation. The Spo0 mutation studied seems to result in a modification of the membrane, such that insertion of Nar A in the modified membrane confers to the enzyme new allotopic properties. Additional and abnormal enzyme-binding sites may be created as a result of the mutation and these may be normalized during heat activation.